TLF6391

June 1989

54LS138DM54LS138DM74LS138

54LS139DM54LS139DM74LS139

DecodersDemultiplexers

General Description

These Schottky-clamped circuits are designed to be used in

high-performance memory-decoding or data-routing appli-

cations requiring very short propagation delay times In

high-performance memory systems these decoders can be

used to minimize the effects of system decoding When

used with high-speed memories the delay times of these

decoders are usually less than the typical access time of the

memory This means that the effective system delay intro-

duced by the decoder is negligible

The LS138 decodes one-of-eight lines based upon the con-

ditions at the three binary select inputs and the three enable

inputs Two active-low and one active-high enable inputs

reduce the need for external gates or inverters when ex-

panding A 24-line decoder can be implemented with no ex-

ternal inverters and a 32-line decoder requires only one

inverter An enable input can be used as a data input for

demultiplexing applications

The LS139 comprises two separate two-line-to-four-line de-

coders in a single package The active-low enable input can

be used as a data line in demultiplexing applications

All of these decodersdemultiplexers feature fully buffered

inputs presenting only one normalized load to its driving

circuit

All inputs are clamped with high-performance

Schottky diodes to suppress line-ringing and simplify system

design

Features

Y

Designed specifically for high speed

Memory decoders

Data transmission systems

Y

LS138 3-to-8-line decoders incorporates 3 enable in-

puts to simplify cascading andor data reception

Y

LS139 contains two fully independent 2-to-4-line decod-

ersdemultiplexers

Y

Schottky clamped for high performance

Y

Typical propagation delay (3 levels of logic)

LS138

21 ns

LS139

21 ns

Y

Typical power dissipation

LS138

32 mW

LS139

34 mW

Y

Alternate

MilitaryAerospace

devices

(54LS138

54LS139) are available Contact a National Semicon-

ductor Sales OfficeDistributor for specifications

Connection Diagrams

Dual-in-Line Package

TLF6391 – 1

Order Number 54LS138DMQB 54LS138FMQB

54LS138LMQB DM54LS138J DM54LS138W

DM74LS138M or DM74LS138N

See NS Package Number E20A J16A

M16A N16E or W16A

Dual-in-Line Package

TLF6391 – 2

Order Number 54LS139DMQB 54LS139FMQB

54LS139LMQB DM54LS139J DM54LS139W

DM74LS139M or DM74LS139N

See NS Package Number E20A J16A

M16A N16E or W16A

C1995 National Semiconductor Corporation

RRD-B30M105Printed in U S A